If your typical workout routine never changes, you're missing out. Here's what you should be doing at the gym, based on your goals and your age

"There are so many benefits to getting in great shape even before you get pregnant," says Trink. "It will give you stamina and stability throughout your pregnancy and the childbirth process, and it will make getting back into shape after you give birth so much easier." Core function is especially important while you're carrying extra weight -- it can minimize back strain -- and learning how to activate certain muscles will make it easier to get them back post-pregnancy.

After you've had a baby, Pagano stresses how important it is to get back to your routine as soon as you've been cleared by your doctor. "There's a small window of opportunity when your hormones will actually help you lose a lot of body fat," she says.

I'm in my 20's and I think it's really important to vary your routine and only do things that you enjoy, then you're more likely to stick with it. Also changing up your routine confuses your body and you are less likely to get used to doing the same exercise over and over, then you hit a plateau and have to change your routine. Some days I do Zumba, walk my dog, cardio kick-boxing or a more intense strength training workout. Even if I'm super lazy I'll still fit in a short walk or yoga, once you get going you almost always want to continue. It's good to have a workout buddy, if you know someone is depending on you to show up, you're more likely to follow through. Also check your local parks and recreation. Often they have free classes. Mine offers free yoga and Zumba. They also have great hiking trails which are free, so no need to pay for a gym membership.